1. Field of the Invention
This invention relates to a biped mobile robot.
2. Description of the Related Art
Various technologies relating to biped mobile robots have been proposed, including, for example, those taught by Japanese Laid-open Patent Application Nos. Sho. 62(1987)-97005 and Sho. 62(1988)-97006. Moreover, a review of the prior art shows that various methods have been proposed for effectively absorbing the impact experienced by a biped mobile robot at footfall (touchdown of a foot during biped walking) owing to reaction forces from the ground.
For instance, Japanese Laid-open Patent Application No. Hei. 11(1999)-33941 teaches a technique of absorbing impact at footfall by providing the entire foot with a cushioning member. Among others that have been proposed is that of absorbing the impact at footfall by sharply bending the knee of the free leg when the robot is walking. Still another is that of Japanese Laid-open Patent Application No. Hei. 7(1995)-205069, which teaches a technique of canceling the spin force around the supporting leg by driving the arms during robot walking.
However, none of these prior art technologies provide a satisfactory solution. Assuming a robot weighing 130 kg, the impact received at footfall amounts to more than 300 kgf. An impact of this magnitude cannot be sufficiently absorbed by providing the whole foot with a shock-absorbing member. Moreover, if a soft shock-absorbing member of great thickness is used to cope with the strong impact at footfall, the robot becomes unstable when standing upright.
The technique of bringing the foot down with the knee of the free leg sharply bent can absorb strong footfall impact to some degree but is incapable of absorbing the footfall impact that arises during high-speed walking with long strides, because the knee of the free leg cannot be bent during such high-speed walking. Bending the knee of the free leg at every footfall also increases energy consumption.
In the technique of the aforesaid Japanese Laid-open Patent Application No. Hei. 7(1995)-205069 of canceling the spin force around the supporting leg by driving the arms during robot walking, the fact that the differing heights of the right and left feet during walking makes the robot body lean, causing the robot to swing laterally during walking. The robot""s posture therefore becomes unstable during high-speed walking. Another problem is that the leaning of the body causes the gyroscope and/or G sensor (accelerometer) mounted on the body""s back or head to output false signals that make walking control difficult. The driving of the arms also consumes additional energy.
A practical technology enabling absorption and mitigation of such footfall impact would expand the degree of freedom in robot gait design, enable rapid, energy-efficient locomotion in a stable attitude, and, by permitting free body movements, make it possible for the robot to work in, for example, a kneeling attitude.
An object of this invention is therefore to provide a biped mobile robot that can effectively absorb and mitigate footfall impact, offer a high degree of freedom in gait design, thereby enabling rapid, energy-efficient locomotion in a stable attitude, and permit free body movement.
For realizing this object, the present invention provides a biped mobile robot having at least a body and two leg links connected to the body; wherein the improvement comprises: a parallel linkage is provided between the body and the two leg links to connect the body to the two leg links such that each of the two leg links are movable relative to the body in a direction of gravity axis.